雙金屬表面上硼氫化物催化產(chǎn)氫的理論研究
發(fā)布時(shí)間：2019-04-04 20:31
【摘要】：近年來,硼氫化物(BH4-)水解反應(yīng)產(chǎn)氫憑借其產(chǎn)氫效率高、原料廉價(jià)易得、能耗低等特點(diǎn)而來備受矚目。BH4-水解催化劑的研究是將BH4-水解產(chǎn)氫技術(shù)進(jìn)一步發(fā)展的重要環(huán)節(jié)。目前,常見的BH4-水解產(chǎn)氫催化劑多以貴金屬為主,催化劑價(jià)格昂貴,不易推廣。在本文工作中,采用量子化學(xué)方法,從原子尺寸上對兩種合金催化劑進(jìn)行了研究考察,以DFT計(jì)算為主要研究手段,系統(tǒng)闡述了 Ir-Ni、Ru-Ni金屬表面催化體系的結(jié)構(gòu)及對BH4-水解產(chǎn)氫反應(yīng)的催化性能。本文主要進(jìn)行了三方面的工作:一是利用DFT計(jì)算對BH4-在Ir-Ni合金表面上的吸附結(jié)構(gòu)、吸附強(qiáng)度和H解離進(jìn)行研究;二是利用DFT計(jì)算研究環(huán)境因素對BH4-在Ir-Ni合金表面上的吸附的影響;三是基于BH4-的水解機(jī)理,利用DFT計(jì)算對不同Ru-Ni合金結(jié)構(gòu)的催化活性研究。本文研究主要獲得以下結(jié)論:(1)通過DFT計(jì)算考察了 BH4-在不同合金表面的吸附結(jié)構(gòu)。結(jié)果表示我們可以通過改變合金表面Ir原子的摻雜比例對BH4-吸附時(shí)的H原子解離情況進(jìn)行調(diào)控。在吸附強(qiáng)度方面,我們得到幾種合金表面對BH4-的吸附強(qiáng)度遵循 IrNi2-Ni (111) 2Ir-Ni (111) Ir2Ni-Ni (111) 1Ir-Ni (111) 1Ir-2Ir2Ni-Ni (111), 1Ir-Ni (111)和 1Ir-2Ir2Ni-Ni (111)兩種合金表面所表現(xiàn)出的BH4-吸附強(qiáng)度接近甚至超過純Ir表面。我們進(jìn)一步通過對合金結(jié)構(gòu)的電子結(jié)構(gòu)的計(jì)算對這一結(jié)果進(jìn)行了證實(shí)與解釋。除此之外,我們還對1Ir-Ni(111)和1Ir-2Ir2Ni-Ni(111)表面上解離后的BH的進(jìn)一步解H反應(yīng)進(jìn)行了機(jī)理研究,結(jié)果與純Ir表面進(jìn)行對比得到,1Ir-2Ir2Ni-Ni(111)結(jié)構(gòu)上此解離反應(yīng)的能壘最小,表明1Ir-2Ir2Ni-Ni(111)合金結(jié)構(gòu)對BH4-的解離具有更高的活性。本項(xiàng)工作可對BH4-水解合計(jì)催化劑設(shè)計(jì)提供部分理論基礎(chǔ)。(2)本文通過DFT方法系統(tǒng)的討論的一系列環(huán)境因素對BH4-在金屬催化劑表面吸附的影響。從吸附結(jié)構(gòu)上來看,H2O分子的加入會促進(jìn)BH4-中H原子的解離,當(dāng)加入OH-存在時(shí),H2O分子對H原子解離的促進(jìn)效果將被削弱。不僅如此,當(dāng)水分子以解離的形態(tài)(H + OH-)存在時(shí),對BH4-吸附的影響則變得十分微弱。從吸附強(qiáng)度上進(jìn)行考察發(fā)現(xiàn),無論是H2O分子的存在還是OH-的存在都會使BH4-與表面的相互作用減弱,進(jìn)一步的電荷分析證實(shí),當(dāng)有其他物質(zhì)共吸附時(shí),催化劑與BH4-之間的電荷遷移會相對減少,使得BH4-的吸附強(qiáng)度變?nèi)�。但這種影響在不同的合金表現(xiàn)上所表現(xiàn)出的強(qiáng)弱不盡相同,因此通過本項(xiàng)研究可以有助于我們更好的篩選穩(wěn)定性更好的催化劑結(jié)構(gòu)。(3)本文DFT計(jì)算對BH4-在Ru-Ni合金表面的水解機(jī)理進(jìn)行了研究,并與純Ru表面上的結(jié)果進(jìn)行了對比。本項(xiàng)工作通過DFT計(jì)算探究了BH4-及其水解過程中各物質(zhì)在Ru-Ni合金表面的吸附結(jié)構(gòu)與吸附強(qiáng)度,發(fā)現(xiàn)在1Ru-2Ru2Ni-Ni(111)合金表面上BH4-中的H原子表現(xiàn)出了解離結(jié)構(gòu),這種結(jié)構(gòu)在純Ru表面并未發(fā)現(xiàn)。進(jìn)一步探究金屬催化劑催化活性發(fā)現(xiàn),針對BH4-的第一步水解,1Ru-2Ru2Ni-Ni(111)合金表面表現(xiàn)出了比Ru(111)表面更好的催化活性。
[Abstract]:In recent years, the hydrolysis reaction of borohydride (BH4-) has attracted attention by the characteristics of high hydrogen production efficiency, cheap and easily available raw materials, low energy consumption and the like. The research of BH4-hydrolysis catalyst is an important part of the further development of BH4-hydrolyzed hydrogen-producing technology. At present, the common BH4-hydrolyzed hydrogen-producing catalyst is mainly a noble metal, the catalyst is expensive and is not easy to popularize. In this paper, a quantum chemical method was used to study the two kinds of alloy catalysts from the atomic size, and the structure of the catalyst system of the metal surface of Ir-Ni and Ru-Ni and the catalytic performance of the hydrogen-producing reaction to the BH4-hydrolysis were described. The first is to study the adsorption structure, adsorption strength and H dissociation of BH4-on the surface of Ir-Ni alloy by means of DFT. The second is to study the influence of environmental factors on the adsorption of BH4-on the surface of Ir-Ni alloy by means of DFT. Thirdly, based on the hydrolysis mechanism of BH4-, the catalytic activity of different Ru-Ni alloy structures was studied by means of DFT. The main results are as follows: (1) The adsorption structure of BH4-on the surface of different alloys is investigated by DFT. The results show that we can control the dissociation of H atoms at the time of BH4-adsorption by changing the doping ratio of the Ir atoms on the surface of the alloy. The adsorption of BH4-Ni (111) Ir2Ni (111) 2Ir-Ni (111) Ir2Ni-Ni (111) 1Ir-Ni (111) 1Ir-2Ir2Ni-Ni (111), 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) on the adsorption strength is close to or above the pure Ir surface. We further confirm and explain this result by the calculation of the electronic structure of the alloy structure. In addition, the mechanism of the further deionization of BH in the surface of 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) is studied. The results are compared with the pure Ir surface, and the energy barrier of the dissociation reaction on the 1Ir-2Ir2Ni-Ni (111) structure is the least, indicating that the structure of the 1Ir-2Ir2Ni-Ni (111) alloy has higher activity for the dissociation of BH4-. This work can provide some theoretical basis for the design of the BH4-hydrolysis total catalyst. (2) The influence of a series of environmental factors on the adsorption of BH4-on the surface of the metal catalyst is studied by means of the DFT method. The addition of H2O molecules can promote the dissociation of H atoms in the BH4-H from the adsorption structure. When OH-is added, the effect of H2O molecules on the dissociation of H atoms will be weakened. Furthermore, when water molecules are present in dissociated form (H + OH-), the influence on BH4-adsorption becomes very weak. It is found that the interaction of the BH4-with the surface is weakened by the presence of H2O molecules or the presence of OH-, and further charge analysis proves that the charge migration between the catalyst and the BH4-is relatively reduced when the other substances are co-adsorbed. Such that the adsorption strength of bh4-is weakened. But this effect is different in different alloy performance, so this study can help us to better screen the catalyst structure with better stability. (3) The hydrolysis mechanism of BH4-on the surface of Ru-Ni alloy is studied by DFT calculation, and the results are compared with the results on the pure Ru surface. The adsorption structure and adsorption strength of each substance on the surface of Ru-Ni alloy in BH4-and its hydrolysis process are investigated by means of DFT calculation, and it is found that the H atoms in BH4-in the surface of the 1Ru-2Ru2Ni-Ni (111) alloy show off-structure, and this structure is not found on the pure Ru surface. Further investigation of the catalytic activity of the metal catalyst found that the surface of the 1Ru-2Ru2Ni-Ni (111) alloy exhibited better catalytic activity than that of the Ru (111) surface for the first hydrolysis of BH4-.
【學(xué)位授予單位】：北京化工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TQ116.2
[Abstract]:In recent years, the hydrolysis reaction of borohydride (BH4-) has attracted attention by the characteristics of high hydrogen production efficiency, cheap and easily available raw materials, low energy consumption and the like. The research of BH4-hydrolysis catalyst is an important part of the further development of BH4-hydrolyzed hydrogen-producing technology. At present, the common BH4-hydrolyzed hydrogen-producing catalyst is mainly a noble metal, the catalyst is expensive and is not easy to popularize. In this paper, a quantum chemical method was used to study the two kinds of alloy catalysts from the atomic size, and the structure of the catalyst system of the metal surface of Ir-Ni and Ru-Ni and the catalytic performance of the hydrogen-producing reaction to the BH4-hydrolysis were described. The first is to study the adsorption structure, adsorption strength and H dissociation of BH4-on the surface of Ir-Ni alloy by means of DFT. The second is to study the influence of environmental factors on the adsorption of BH4-on the surface of Ir-Ni alloy by means of DFT. Thirdly, based on the hydrolysis mechanism of BH4-, the catalytic activity of different Ru-Ni alloy structures was studied by means of DFT. The main results are as follows: (1) The adsorption structure of BH4-on the surface of different alloys is investigated by DFT. The results show that we can control the dissociation of H atoms at the time of BH4-adsorption by changing the doping ratio of the Ir atoms on the surface of the alloy. The adsorption of BH4-Ni (111) Ir2Ni (111) 2Ir-Ni (111) Ir2Ni-Ni (111) 1Ir-Ni (111) 1Ir-2Ir2Ni-Ni (111), 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) on the adsorption strength is close to or above the pure Ir surface. We further confirm and explain this result by the calculation of the electronic structure of the alloy structure. In addition, the mechanism of the further deionization of BH in the surface of 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) is studied. The results are compared with the pure Ir surface, and the energy barrier of the dissociation reaction on the 1Ir-2Ir2Ni-Ni (111) structure is the least, indicating that the structure of the 1Ir-2Ir2Ni-Ni (111) alloy has higher activity for the dissociation of BH4-. This work can provide some theoretical basis for the design of the BH4-hydrolysis total catalyst. (2) The influence of a series of environmental factors on the adsorption of BH4-on the surface of the metal catalyst is studied by means of the DFT method. The addition of H2O molecules can promote the dissociation of H atoms in the BH4-H from the adsorption structure. When OH-is added, the effect of H2O molecules on the dissociation of H atoms will be weakened. Furthermore, when water molecules are present in dissociated form (H + OH-), the influence on BH4-adsorption becomes very weak. It is found that the interaction of the BH4-with the surface is weakened by the presence of H2O molecules or the presence of OH-, and further charge analysis proves that the charge migration between the catalyst and the BH4-is relatively reduced when the other substances are co-adsorbed. Such that the adsorption strength of bh4-is weakened. But this effect is different in different alloy performance, so this study can help us to better screen the catalyst structure with better stability. (3) The hydrolysis mechanism of BH4-on the surface of Ru-Ni alloy is studied by DFT calculation, and the results are compared with the results on the pure Ru surface. The adsorption structure and adsorption strength of each substance on the surface of Ru-Ni alloy in BH4-and its hydrolysis process are investigated by means of DFT calculation, and it is found that the H atoms in BH4-in the surface of the 1Ru-2Ru2Ni-Ni (111) alloy show off-structure, and this structure is not found on the pure Ru surface. Further investigation of the catalytic activity of the metal catalyst found that the surface of the 1Ru-2Ru2Ni-Ni (111) alloy exhibited better catalytic activity than that of the Ru (111) surface for the first hydrolysis of BH4-.
【學(xué)位授予單位】：北京化工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TQ116.2
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